Representative apparatuses for sensing a user's motion for pointing at or inputting information in a two- or three-dimensional space are handheld space-type input apparatuses, such as personal computers (PCs), personal digital assistances (PDAs), and cellular phones; wireless portable pointing apparatuses, wireless portable keyboards; hand motion and gesture recognizing apparatuses; virtual musical playing apparatuses; computer game machines; virtual environment exercise and training apparatuses; virtual reality data gloves; mechanical impact and shake tracking and monitoring apparatuses; and robot motion information acquiring apparatuses.
Usually, in order to determine whether information generated by a user's motion using the above apparatuses is effective, conventionally, a mechanical switch or a pressure sensor is used. In other words, according to a conventional method, when a switch or sensor is pushed or touched on a plane, an on/off signal is generated, and effective information is identified according to the on/off signal. Conventionally, whether a user's motion for selecting information is an effective one can be determined by contact on a plane, but whether a user's motion for selecting information in a three-dimensional space is an effective one cannot be determined via the same method.